Juglans nigra, or the Black Walnut, is a large, robust deciduous tree native to eastern North America but found growing in England and other parts of the world. Despite its origins, this species has adapted well to the British climate and is appreciated for its grand stature, handsome foliage, and valuable timber.
The Black Walnut tree typically grows to a height of 30-40 metres, boasting a wide-spreading, rounded crown that gives it a majestic appearance. Its bark is deeply furrowed and dark brown to black, contributing to the tree’s name. The pinnate leaves consist of 15-23 leaflets, each up to 10cm long, that offer a beautiful bright green hue in the summer, turning yellow in the autumn.
The Black Walnut produces male and female flowers on the same tree, a characteristic known as monoecy. The male flowers are slender, drooping catkins that appear in spring, while the female flowers are smaller and occur in clusters at the tips of the branches. Upon pollination by wind, the female flowers develop into round, green fruits encased in a thick husk. The husks turn black and drop in the autumn, revealing the hard-shelled nut inside.
The Black Walnut exhibits a moderate to fast growth rate and can live up to 200 years, and some specimens have even been known to live longer. They often take around 10-20 years to begin producing nuts, with full nut-bearing potential reached at around 30 years.
Compared to other trees in England, the Black Walnut stands out with its large size, dark bark, and the rich, chocolate-brown wood it produces, which is highly prized in furniture making and woodturning. The production of edible nuts is another distinguishing feature of this tree.
In a British garden design context, the Black Walnut is an impressive choice as a specimen tree in large gardens or parks due to its size and grandeur. Its spreading canopy provides excellent shade, and its distinctive leaves create beautiful autumn colour.
As for wildlife benefits, the Black Walnut tree’s catkins provide pollen for insects, while the nuts are sought after by squirrels, mice, and some bird species. The tree’s canopy provides shelter and potential nesting sites for birds.
A fascinating characteristic of Black Walnut trees is their allelopathic nature. They release a chemical known as juglone into the soil, which can inhibit the growth of certain other plants nearby. While this makes companion planting a bit of a challenge, it can also be used advantageously in landscape design to control the growth of less desirable species.
In summary, Juglans nigra, the Black Walnut, is a majestic and versatile tree. It not only impresses with its size and appearance but also provides tangible benefits in the form of timber and nuts. Its ecological contributions and the dynamic it introduces into the garden landscape make it a worthwhile addition to British gardens.